The present invention relates to a quietly operating pump assembly which is effective to reduce the torque required to drive it when a predetermined operating speed is exceeded.
Prior to the making of the invention disclosed herein, it was suggested that the size of the inlet to a slipper pump could be reduced to limit the rate at which liquid can enter the pump. Limiting the inlet flow rate would decrease the torque required to drive the pump at relatively high speeds. It was also suggested that the slippers be mounted to prevent a back flow of fluid from the pump outlet into pumping chambers other than the chamber at the pump outlet. With such an arrangement, each slipper would be disposed in a recess in a rotor. The slipper would sealingly engage both the trailing edge of its rotor recess and a cam ring encircling the rotor. Therefore the slippers blocked a back flow of fluid from the pump outlet to the pumping chambers other than the pumping chamber at the pump outlet. This suggested pump design did not have plural outlet openings or check valves separate from the slippers of the pump. In addition, this suggested pump was noisy and had a fluctuating fluid pressure output.
U.S. Pat. No. 3,790,307 discloses a pump having hollow pistons which internally define pumping chambers. The pumping chambers move along a circular path circumscribed by a cam ring. In sequential portions of their movement, the chambers move past a series of inlet openings and a series of outlet openings. A plurality of check valves in the outlet openings prevent a flow of fluid from the outlet of the pump back into the pumping chambers. When the fluid pressure in the pumping chambers exceeds the outlet fluid pressure, the check valves open and fluid flows from the chambers to the pump outlet.